Posterior ligamentous complex (PLC) components have an orderly sequence of rupture. However, it is still unclear how many structures have to be damaged to consider it disrupted. We aim to establish imaging criteria, which can define the complex as competent or incompetent.

Prospective study of 74 consecutive vertebral acute traumatic fractures, using X-rays and MRI scan (FS-T2-w/STIR sequences). We analyzed the association between MRI signal (intact, edema, disruption) of each PLC component-facet capsules (FC), interspinous ligaments (ISL), supraspinous ligaments (SSL) and ligamentum flavum (LF)-and the variables: AO/TLICS classification, treatment, surgical findings, interspinous diastasis index (IDI), local kyphosis (LVK) and ISS (TLICS) score. χ2 test and U Mann-Whitney were used for statistics.

MR images of ISL edema correlated surgically with intact ligaments or laxity, and were associated with 87.5% of facet distraction, LVK: 11.6º, IDI: 1.2. Images of ISL, SSL or LF disruptions showed in all cases ruptures under surgical examination. Images of SSL disruption associated with LVK: 14.5º, IDI: 1.8. Images of ISL disruption associated with SSL/LF rupture, LVK: 16º, and IDI: 2; while LF disruption showed LVK: 18º, IDI: 1.9. When comparing "competent PLC" (images of facet distraction and ISL edema) with "incompetent PLC" (images of SSL disruption ± ISL or LF disruption) the latest showed more severe scores in every variable (p < 0.001), except neurologic status.

Following PLC rupture sequence, ISL edema with facet distraction seems not to be enough to define a posterior tension band incompetence. It is the further step of SSL rupture what gives the key to PLC incompetence.